At present, in China, the majority of power distribution cabinet are provided with a .DELTA./Y.sub.0 connected three-phase three-leg distribution transformer, while high voltage load switches, tapping switches, high voltage fuses (or circuit breakers) etc. are installed outside the sealed enclosure of the distribution transformer. As a result, the power distribution cabinet used in China has a larger volume, occupies more land and needs more maintenance. In the United States, an integrated power distribution cabinet, in which a Y.sub.0 /Y.sub.0 connected three-phase five-leg distribution transformer is mounted, is popularly used, wherein the main bodies of high voltage load switches, tapping switches, and high voltage fuses are installed inside the sealed enclosure of the distribution transformer. Hence, the power distribution cabinet used in the United States has a smaller volume, occupies less land and needs less maintenance. However, the integrated power distribution cabinet has a disadvantage that it can not be used in a neutral non-grounded power system. Because in a neutral non-grounded power system, whether the transformer is connected in a Y.sub.0 Y.sub.0 connection mode or in a .DELTA./Y.sub.0 connection mode, interrupting of one phase of high voltage fuse will cause the other two phases to have supply voltages far higher or far lower than the rated voltages thereof. It not only impairs the quality of power supply, but also probably causes damages of the user's electric apparatus as operating under such a higher voltage or lower voltage. For the time being, in China, a solution is to trip simultaneously all three phases artificially when an one-phase fault occurs. Obviously it is not very reasonable.